docs: def set_regionfiles(self, filenames):
          """
          This method directly sets the region files for this instance to use.
          It assumes the filenames are in the form r.<x-digit>.<z-digit>.<extension>
          """
          for filename in filenames:
              # Assume that filenames have the name r.<x-digit>.<z-digit>.<extension>
              m = re.match(r"r.(\-?\d+).(\-?\d+)."+self.extension, os.path.basename(filename))
              if m:
                  x = int(m.group(1))
                  z = int(m.group(2))
              else:
                  # Only raised if a .mca of .mcr file exists which does not comply to the
                  #  r.<x-digit>.<z-digit>.<extension> filename format. This may raise false
                  # errors if a copy is made, e.g. "r.0.-1 copy.mca". If this is an issue, override
                  # get_filenames(). In most cases, it is an error, and we like to raise that.
                  # Changed, no longer raise error, because we want to continue the loop.
                  # raise UnknownWorldFormat("Unrecognized filename format %s" % os.path.basename(filename))
                  # TODO: log to stderr using logging facility.
                  pass
              self.regionfiles[(x,z)] = filename